Morphologically, this population appears to be distinct (Groves 2001). Acoustically, it shows many obvious superficial similarities with T. dentatus and might be related to that species (A. Nietsch and F. Burton unpubl. data). A. Nietsch (pers. comm.) nevertheless found the acoustics to be distinctive, in spite of the overall similarity.

Justification:
This species is considered Endangered as the species is known to occur only on Peleng island. Over this range it occurs in a number of fragmented populations, and a there is believed to be a continued decline in extent and quality of its habitat, and its extent of occurrence is less that 5,000 km².

This species is found on Peleng Island (Sody 1949), off the coast of the eastern peninsula of Sulawesi. There are unconfirmed reports that tarsiers might be present in other islands of the nearby Banggai Archipelago, and if these reports are accurate, then this would extend the range of T. pelengensis.

This taxon has not been studied in the wild. By analogy with other taxa of eastern tarsiers, we can estimate that densities in good habitat might be 156/km2 (Gursky 1997), or, as for T. dentatus (Merker 2003) up to 270/km2 in pristine habitat, 190/km2 for slightly disturbed, 130/km2 for moderate disturbance, and 45/km2 in heavily disturbed habitat.

This species is believed to inhabit primary and secondary lowland and mangrove forest (to 520 m) (M. Indrawan and Y. Masala pers. comm.). Like all tarsiers it shows extreme adaptations for vertical clinging and leaping (VCL) in the understory of suitable tropical habitats, often 2 meters or less from the ground. Nocturnal, social primates, they are likely to live in small, monogamous or polygamous groupings of 2-6. Their diet is 100% live animal prey, mostly insects with some small vertebrates.

GIS estimates indicate that only 211 km2 of “good” habitat remains on Peleng Island (2,339 km2). This implies that perhaps as little as 9% of the original habitat of the island remains in good condition. Therefore it seems likely that, while we know little about this species, habitat loss through slash and burn activities is a major threat. On the other hand, it is not clear that “good” habitat is also compatible with the needs of tarsier conservation. All species of tarsiers that have been studied in the wild are recorded in a number of non-forest habitats, but it remains an open question as to whether these habitats are suitable for sustainably-reproducing populations. GIS also provides an estimate of 1,474 km2 of “fair” habitat remaining on Pulau Peleng. Together with “good” habitat, this yields a total of 1,685 km2 of habitat that is potentially suitable for tarsier conservation, a figure that represents slightly more than 72% of the island’s total area. In other words, the estimate of the percentage of the original tarsier habitat that still remains on Pulau Peleng varies from 9 to 72%, depending on whether “fair” habitat is included in the model. This example illustrates the need for field surveys to determine the suitability of “fair” habitat for sustainable tarsier populations. In the meantime, we use a most conservative estimate that includes good habitat only.

First-hand reports of conditions on Pulau Peleng are scant, but by analogy with other areas of Sulawesi, it should likely expect a continuing pattern of encroachment into tarsier habitat, leading to a decrease in the area of occupancy, quality of habitat, number of tarsier populations and mature individuals (M. Shekelle pers. comm.). Other threats may include illegal logging, agricultural pesticides, and predation by domestic animals (dogs and cats).